Previously, the generate-fixtures shell script by called into Django
multiple times in order to check whether the database was in a
reasonable state. Since there's a lot of overhead to starting up
Django, this resulted in `test-backend` and `test-js-with-casper`
being quite slow to run a single small test (2.8s or so) even on my
very fast laptop.
We fix this is by moving the checks into a new Python library, so that
we can avoid paying the Django startup overhead 3 times unnecessarily.
The result saves about 1.2s (~40%) from the time required to run a
single backend test.
Fixes#1221.
Tomasz Kolek